Several conventional drive sources are used for joint drive mechanisms of industrial robots including electromagnetic motors, hydraulic actuators, and pneumatic actuators. The joint drive mechanisms using these drive sources, which include those using electromagnetic motors and reduction mechanisms mainly made from metals and those using metal hydraulic/pneumatic cylinders, are themselves made of hard and heavy materials and are managed and used in specific locations within factories.
Drive sources of apparatuses such as robots which are expected to operate near the presence of human beings for housekeeping assistance, job assistance, and nursing help for elderly and physically-challenged persons in homes, offices, and hospitals, are required to be small, light, flexible, safe.
Examples of such actuators include a rubber pneumatic actuator having high flexibility among the pneumatic actuators, though this actuator requires auxiliary equipment such as compressors and control valves for driving, which limits weight reduction of the entire system.
Accordingly, an artificial muscle actuator using various kinds of polymer materials which have light weight and high flexibility has been proposed, and its practical application is much desired.
A polymer actuator operated by electric impulses is described in the keynote speech in Non Patent Document 1 (S G. Wax, R. R. Sands, Smart Structures And Materials 1999: Electroactive Polymer Actuators and Devices, Proc. SPIE, Vol. 3669, pp. 2-10, 1999). A conference concerning research in this field is held annually, and active research efforts are being made. The research is about polymer actuators, which are made of polymer gels, metal composite ion polymers, organic conductive polymers, carbon dispersion conductive polymers, dielectric elastomers, and the like which are driven by electric impulses. Among these, the conductive polymers such as the organic conductive polymers and the carbon dispersion conductive polymers can be driven at relatively low voltage and generate stress having a capacity larger than living body muscles, and have characteristics such as light weight and flexibility.
As an example of the conductive polymers, Patent Document 1 (Japanese Unexamined Patent Publication No. H11-169394) discloses an actuator manufactured by forming metal electrodes on a polyaniline film article that is an organic conductive polymer and sandwiching the metal electrode between solid electrolyte molding objects. While the organic conductive polymers themselves have conductivity and so a voltage can be applied by using these as electrodes, the metal electrodes are formed for the purpose of avoiding voltage drop caused by resistance of the conductive polymers. By applying a voltage to between these electrodes, anions in the solid electrolyte molding objects move from the cathode to the anode, as a result of which the polyanilines in the anodes are doped with anions and swell. Contrary to this, the polyanilines in the cathode are subject to the reverse action, that is, the anions are separated from the polyanilines and the polyanilines shrink. As a result, the actuator composed of the conductive polymer and the polyaniline film article is curved. This is a phenomenon of the thin film article being deflected to provide a large displacement, though the deflection rigidity is too low to produce large forces.
An example of the actuator in which a conductive polymer is not deformed by deflection but deformed by expansion and contraction in its longitudinal direction, and in which an organic conductive polymer is attached to a metallic coil spring as an electrode is disclosed in Non Patent Document 2 (Gordon G. Wallace etc., Smart Structures And Materials 2002: Electroactive Polymer Actuators and Devices, Proc. SPIE, Vol. 4695, pp. 8-16, 2002.). The organic conductive polymer is a cylinder shape, resulting in a small effective cross-sectional area for generating generative force in a bundle. Further in this example, a cylinder-shaped conductive polymer with a coil spring is structured to be housed in a cylinder-shaped container in order to seal an electric field liquid, which further decreases the effective cross-sectional area. Moreover, a force action portion is structured so as to be combined with a movable pin and a spring, which complicates manufacturing.
Moreover, Patent Document 2 (Japanese Unexamined Patent Publication No. H07-83159) and Patent Document 3 (Japanese Unexamined Patent Publication No. H06-133922) each disclose an actuator having an electrode formed into a cylinder shape which performs flexing actions by electric impulses. In both cases, the actuator is formed into a cylinder shape or a coiled shape with a large thickness, which causes the actuator to have poor responsivity, to operate only at low speed, and which makes its manufacturing difficult.
The term “conductive polymers” is herein used to broadly refer to conductive polymers including an organic conductive polymer in which the polymer itself has conductivity and a conductive polymer doped with conductive materials such as carbon particles.